The Ni–metal-induced lateral crystallization (NILC) of amorphous silicon (a-Si) has been used to fabricate low-temperature polycrystalline silicon thin-film transistors. Three stages have been identified in the NILC process: (1) the formation of NiSi2 precipitates, (2) the nucleation of crystalline Si (c-Si) on NiSi2 precipitates, and (3) the subsequent migration of NiSi2 precipitates and growth of c-Si. In this study, a bending fixture was used to investigate the effects of tensile stress on the growth of NILC. It was found that tensile stress did not enhance NiSi2 formation and c-Si nucleation stages, but enhanced the c-Si growth stage. It was also found that compressive stress did not change NILC rate.
Ni-metal-induced lateral crystallization (NILC) of amorphous silicon (-Si) has been employed to fabricate high-performance low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs). However, the current crystallization technology often leads to trapped Ni and NiSi 2 precipitates, thus degrading the device performance. We proposed using -Si-coated wafers as Ni-gettering substrates. By bonding the gettering substrate and NILC poly-Si film together, the Ni-metal impurity within the NILC poly-Si film was greatly reduced.
Comparison of low-temperature polycrystalline silicon ͑poly-Si͒ thin-film transistors ͑TFTs͒ fabricated by both IMPRINT and IMPRINT-excimer loser annealing ͑ELA͒ methods was investigated. IMPRINT poly-Si was fabricated by pressing imprint mold ͑coated with Ni film͒ together with amorphous Si film and then annealing at 550°C. After the sample stack was separated, IMPRINT poly-Si film was irradiated by an excimer laser to form IMPRINT-ELA poly-Si. Upon increasing the laser energy to 345 mJ/cm 2 , the performance of IMPRINT-ELA-TFT was found to be far superior to that of IMPRINT-TFT due to larger grains and fewer intragrain defects of the IMPRINT-ELA poly-Si film than that of the IMPRINT poly-Si film. The mobility of the IMPRINT-ELA-TFT was 413 cm 2 /V s, which was 31.7 times higher than that of the IMPRINT-TFT. The on/off current ratio of the IMPRINT-ELA-TFT was 4.24 ϫ 10 6 , which was two orders magnitude higher than that of the IMPRINT-TFT.Low-temperature polycrystalline silicon ͑LTPS͒ thin-film transistors ͑TFTs͒ have attracted considerable interest due to their use in active matrix liquid crystal displays ͑AMLCDs͒ and active matrix organic light-emitting diodes ͑AMOLEDs͒ 1,2 because they exhibit superior performance compared to amorphous silicon ͑␣-Si͒ TFTs and can be used to integrate circuits on glass substrate. Polycrystalline silicon ͑poly-Si͒ films are usually formed by Ni-metal-induced lateral crystallization ͑NILC͒ 3 or excimer laser annealing ͑ELA͒. 4 The ELA technique appears to be highly promising because of its shorter processing time and low thermal budget. ELA poly-Si film exhibits good crystallinity and few intragrain defects. Although high-performance ELA TFTs with a mobility of over 300 cm 2 /V s have been fabricated, 5 their uniformity is inadequate and the surfaces of their poly-Si films are rough. In the NILC method, a thin Ni layer is selectively deposited on the top of an ␣-Si, which is then crystallized at a temperature lower than 600°C, subsequently forming nickel silicides. The crystallization of poly-Si is proceeded by the migration of nickel silicides through ␣-Si, forming needlelike Si grains. NILC TFTs are also appropriate for AMLCDs. 6 However, the NILC poly-Si film has intragrain defects with some uncrystallized regions between poly-Si grains. These defects degrade the transfer characteristics of TFT devices, including field effect mobility and leakage current. The imprint NILC method 7 has many better characteristics than the traditional NILC method, including fewer branch grains and a higher grain growth rate. However, some ␣-Si regions are present between needle grains. In this work, Ni-imprint Si grains are annealed using an excimer laser to improve the electrical characteristics of the poly-Si films.
Device FabricationTwo types of poly-Si films were investigated in this study. Samples were designated as follows: ͑i͒ "IMPRINT" is a poly-Si film fabricated with the Ni-imprint method, while ͑ii͒ "IMPRINT-ELA" uses the same imprint method with an additional ELA process. The imprin...
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